1. Field of the Invention
The present invention is directed to balanced ionization for static charge neutralization by barrier discharge. Accordingly, the general objects of the invention are to provide novel systems, methods, and apparatus of such character.
2. Description of the Related Art
A significant portion of present semiconductor manufacturing begins with the creation of wafers that are then processed in various ways in a low-pressure/vacuum environment. Such processing may include thin film material deposition, etching, spattering, plasma treatment, and/or other operations running at middle or deep vacuum (i.e., low pressure). In this context middle or deep vacuum pressure is typically between about 10−2 Torr to about 10−3 Torr.
One new trend in semiconductor manufacturing is a transition away from wafer-based manufacturing and to continuous roll to roll manufacturing. Roll to roll semiconductor manufacturing generally entails printing electronic circuits (for example by vacuum metallization) on a suitable thin plastic film as it is unwound from one spool and then wound onto another. Micron and submicron printed electronic circuits are possible using roll to roll manufacturing, but commercially viable implementations must strictly comply with semiconductor quality control requirements that have applied to wafer-based manufacturing. In particular, the resulting work product must be virtually defect-free, uniform, and clean.
The unavoidable generation of electrostatic charges in middle and low pressure roll to roll semiconductor manufacturing environments presents significant problems. These include (1) electrostatic adhesion of the thin film due to handling and/or guiding devices during loading and/or unloading, (2) damaged thin film work product due to high electrical stresses and discharges, and (3) thin film surface contamination due to adhesion of attracted particulates. These problems are expected to become more acute as semiconductor circuitry dimensions decrease and densities increase. Thus, there is growing interest in electrostatic charge generation, monitoring, and neutralization, especially in low pressure roll to roll semiconductor manufacturing.
Corona-based static charge neutralizers designed to operate at normal atmospheric pressure (typically about 760 Torr) are, of course, well known. However, they are generally considered to be undesirable for use in variable and/or middle to low pressure environments because they are prone to electrical breakdowns, spark discharges, and electrode erosion. For these reasons, other technologies have been adopted for use in low pressure semiconductor manufacturing. For example, plasma neutralizers using magnetron-DC discharge or RF type plasma ion generating sources have been used to shower semiconductor wafers with electron/ion beams during ion implantation and/or etching. Also, photo ionizing neutralizers using soft X-ray and UV light generating lamps are known for neutralizing products at low pressure in the presence of inert and electro-positive gases like N2 and Ar. However, the efficiency of photo ionizing neutralizers is known to dramatically decrease at N2 and O2 gas pressures in the range 10−1-10−2 Torr. Finally, UV deuterium lamp neutralizers may provide bipolar ionization and static charge reduction on wafers at reduced pressure down to 10−3-10−5 Torr. Such neutralizers suffer from a number of serious deficiencies. These include the fact that UV deuterium arc lamps (1) operate at very high temperatures, (2) require special high voltage power supplies and efficient cooling systems, and (3) produce relatively narrow neutralization beams that operate across small areas.
Accordingly, further improvements in static charge neutralization in thin film and/or wafer semiconductor manufacturing, especially as performed in middle to low vacuum pressure environments, continue to be desirable.